Glucoamylases, and particularly glucoamylases having granular starch hydrolyzing (GSH) activity are important industrial enzymes used for producing products such as organic acids (i.e. lactic acids), amino acids (i.e. glutamic acids), alcohols (i.e. ethanol) and other compounds from starch substrates derived from grains and cereals. During microbial fermentations, and particularly during simultaneous saccharification and fermentation (SSF), it would be of benefit to reduce the amount of residual starch in the fermentation when granular starch substrates are used as a carbon feed. The present invention answers this need by providing an acid-stable alpha amylase (asAA) having granular starch hydrolyzing activity, which may be used in combination with a glucoamylase to enhance starch hydrolysis and alcohol production.
Additionally, benefits of the present invention over prior art compositions and methods include one or more of the following: a) a reduction of thermal energy use during starch hydrolysis and end-product production; b) reduction in the requirement of high enzyme dosage; c) utilization of a continuous internal glucose feed; d) maintenance of a relatively low glucose level in the fermenter, which significantly reduces the high risk of microbial contamination and removes the catabolite repression of yeast due to high concentration of free glucose; e) reduction in formation of browning reaction products; f) reduction or removal of calcium addition, which was required during the prior art jet cooking process; g) reduction in water utilization during the fermentation process; h) use of higher solids content in the fermentation, which may result in higher end-product formation and reduced energy costs; i) reduced levels of production of certain by-products, such as glycerol; and j) decreased residual starch content of distillers dry grains plus solubles.